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Int.J.Human-Computer Studies 60 (2004) 737–752What makes mobile computer supportedcooperative work mobile?Towards a betterunderstanding of cooperative mobile interactionsGregor Schrotta,*,Johannes Gl.ucklerbaInstitute of Information Systems,Frankfurt University,Mertonstr.17,Frankfurt D-60054,GermanybInstitute for Economic and Social Geography,Frankfurt University,Dantestr.9,Frankfurt D-60054,GermanyAbstractDespite the high availability of mobile phones and personal digital assistants with onlinecapabilities,mobile computer supported cooperative work is still in its infancy.So far,onlylittle is known about the distinct attributes of mobile cooperative work in comparison to itsstationary counterpart.Across which dimensions does cooperation via mobile devices differfrom traditional hard-wired settings and what implications have to be drawn for futureresearch?To bring more light to this question,we conducted an experimental business-case atFrankfurt University with 16 graduate students and analysed their collaborative behaviouracross mobile and non-mobile channels of communication over a 5 week period.We ﬁnd thatmobile messages differed from stationary messages in terms of size and that the use of mobileemails prevailed over stationary emails under conditions of stress.Finally,we found that thesocial structure of mobile communication corresponded with the structure of stationarycommunication.This indicates that mobile communication technologies support existingcommunication relations rather than creating new relations.From the perspective of systemdesigners,these results may serve as practical insights into the user behaviour of mobiletechnologies and might support the future development of mobile computer supportedcooperative work environments.r 2003 Elsevier Ltd.All rights reserved.ARTICLE IN PRESS*Corresponding author.Tel.:+49-69-798-23318;fax:+49-69-798-28585.E-mail addresses:gschrott@wiwi.uni-frankfurt.de (G.Schrott),glueckler@em.uni-frankfurt.de(J.Gl.uckler).1071-5819/$ - see front matter r2003 Elsevier Ltd.All rights reserved.doi:10.1016/j.ijhcs.2003.11.0061.IntroductionMobile work scenarios in which business managers interact with their colleaguesin an ‘anytime,anywhere’ (Johansen,1988) fashion have become reality on a largescale.Several factors have contributed to this development.First,immense effortshave been undertaken towards organizational restructuring in order to reduce thelevel of hierarchy within organizations and to create more permeable internal andexternal boundaries.Unlike in the ‘old days’ employees do not have to be co-locatedwith their colleagues to interact.Instead,the vision of future work scenariosconstitutes settings in which globally distributed individuals may work togethersimultaneously without sharing physical co-presence (Malone and Laubacher,1998).The second factor that has contributed to this development has been the availabilityof technological infrastructure.For example,global system for mobile communica-tion protocol is currently applied in 190 countries of the world on a reliable basis andthe number of worldwide subscribers is expected to exceed the one billion mark atthe end of this year (GSM-World,2003).In Germany,for the ﬁrst time in 2000 thenumber of mobile subscribers was higher than the number of traditional wiredtelephone users (IZT,2001).Third,the number of providers for mobile devices hasbeen increasing steadily.The variety of personal digital assistants with mobile accessand Smartphones has never been greater before.Fourth,the shrinking costs of datatransmission and the sponsoring of devices have additionally catalysed thedistribution of mobile technologies and ampliﬁed the growth of the worldwidemobile market.Together with a strong emphasis on collaboration and group work(Reichwald et al.,2000;Katzenbach and Smith,1993) these factors have led toestablish mobile cooperative work as an integral part of our daily working life.Surprisingly,from a research perspective still little is known about the distinctfeatures of mobile employee collaboration in comparison to workstation-centriccomputer supported cooperative work settings.While several technically orientatedpublications have described innovative systems and prototypes for mobilecollaboration and made valuable suggestions on how to improve the usability ofmobile devices,the socio-technical perspective has not been equally developed(Bellotti and Bly,1996;Fagrell et al.,1999;Fagrell and Ljungberg,2000;Wiberg andGr.onlund,2000).In order to contribute to a better understanding of the interactionand communication processes within mobile computer supported cooperative worksettings,we focused on the following questions:*Do mobile messages differ fromstationary messages with regard to frequency andsize?*Under what conditions do users prefer mobile over stationary communication?*Does mobile communication imply or foster different structural communicationpatterns,i.e.do people use different technologies to relate to different people?We believe that a more comprehensive understanding of users’ behaviour will leadto an improvement of systems development and its applicability.The paper isorganized in ﬁve sections.Section 2 discusses related work in the ﬁeld of mobileARTICLE IN PRESSG.Schrott,J.Gl.uckler/Int.J.Human-Computer Studies 60 (2004) 737–752738computer supported cooperative work and develops the hypotheses for ourargument.Section 3 describes the experiment and the infrastructure used.Afterthat,Section 4 presents the ﬁndings and discusses the results.Section 5 summarizesthe argument and provides an outlook on possible further research.2.Characteristics and consequences of mobile communicationMobile computer supported cooperative work issues have been tackledpredominantly from a technical perspective.The availability of technical infra-structure,devices and software applications certainly forms the prerequisite forwireless collaboration in global system for mobile communication networks.Recently,some economists and business administrators have started working onthe creation of valuable business models and the applications of economic principlesto cooperative multi-player scenarios in the mobile world.Apart from these twostrands of thought,social scientists have raised questions about how the people whohave started to use mobile devices integrate this technology into their daily life andhow mobile technology enables and constrains new patterns of interaction (e.g.Katzand Aakhus,2002).One illustrative example is Muziko Ito’s analysis of how theincreasing availability of mobile communication infrastructure has inﬂuencedthe transformation of the Japanese youth (Ito,2001).In addition to studies on theimpact of communication technology on the social life world,more research isneeded on the integration of mobile communication technology into corporatebusiness processes and work relations.For the near future,the support andassistance of corporate work environments is expected to remain one of the mostimportant applications to satisfy user needs.But what makes mobile computersupported cooperative work different from its stationary counterpart?In this paper,we will focus on three types of differences.First,we take a look at the frequency andvolume of message exchanges;second,we look at the conditions in which mobileemail communication is employed and third,we look at the social structure ofnetworks that mobile communication reﬂects between work collaborators.2.1.Mobile vs.stationary electronic messagesMobile devices differ from stationary personal computers (PCs) along variousattributes.Smaller displays (Brewster,2002),limited input-capabilities (James andReischel,2001) as well as smaller storage capacity and bandwidth (Varshney,1999;Dunlop and Brewster,2002) affect the ergonomics of these devices to a great extent.Pocket PCs are usually equipped with a 240 320 pixels and 4096 colours display,which is very small and limited in comparison to a desktop screen.To enter data,users either have to use a small keyboard or type-recognition both incorporated intothe touch screen,which is much less comfortable than a conventional keyboard.Thebatteries usually last for 4–5 h when extensively using the device.Storage is limited aswell.Despite the possibility of expanding the standard storage through media-cards,most devices on the market currently offer 32–64 megabyte for data storage.ARTICLE IN PRESSG.Schrott,J.Gl.uckler/Int.J.Human-Computer Studies 60 (2004) 737–752 739Another important factor is the limited bandwidth.When using plain global systemfor mobile communication protocol or general packet radio services protocol,thebandwidth is far smaller than the usual internet connection.All these factors make itsomewhat ‘inconvenient’ for the collaborators to use mobile devices for electronicmessaging.It seems obvious that limited comfort and capacity of mobile deviceshave consequences on the intensity and structure of communication facilitatedacross this medium.Therefore,one would expect messages that are sent via mobiledevices to differ from stationary emails with regard to frequency and size.Thelimited input–output capabilities of mobile devices and other limitations mentionedabove are assumed to have an effect on the emails sent via these devices.We expectusers to write shorter messages over mobile channels.Apart fromdifferences inducedby different ergonomics,the situations in which mobile devices are used to exchangeemail messages will play an important role,too.2.2.Situation dependenceSeveral authors have described the speciﬁcs and advantages of mobile services ingeneral (B.ullingen and W.orter,2000;Gerpott,2001;Reichwald et al.,2002;Kollmann,2001;M.uller-Veerse,1999;Schmitzer and Butterwege,2000;Wiedmannet al.,2000;Wohlfahrt,2001;Zobel,2001).Apart fromthe independence of location,instant connectivity is articulated as a core feature of mobile services compared toconventional desktop applications.When looking at marketing campaigns from themajor mobile operators and research studies,one can easily see that it is on top ofusers’ wishes to be able to receive emails formother colleagues without delay (Hyers,2001).However,given the inconvenience of the application of this technology,mobile communication over small devices is not yet capable of entirely replacingstationary communication over conventional desktops.In turn,when communica-tion is urgent and stationary infrastructure is not available,we expect mobile devicesto be used more frequently.More generally we suggest that under conditions ofstress and the need for immediate communication,the use of mobile technology foremail exchanges will increase.If the saying ‘time is money’ is right,then professionalcollaborators will prefer mobile communication channels to save time and prefermobile exchanges of email if time is short.2.3.Social structures of communicationKnowledge ofﬁcers who are responsible for the successful management ofcomputer supported cooperative work environments have to care for various tasks.Apart from the design of computer supported cooperative work platforms (Pinelieand Gutwin,2000) and soft-skill matching for successful team formation (F.arberet al.,2003),an analysis of the underlying communication structure is believed tocontribute to a better understanding of dynamics within these communicationnetworks.Furthermore,knowledge of the social structure of communicationrelations would allow for a more subtle understanding of how to improve workorganization (Cross et al.,2001;Cross and Prusak,2002).However,analysingARTICLE IN PRESSG.Schrott,J.Gl.uckler/Int.J.Human-Computer Studies 60 (2004) 737–752740communication networks is a difﬁcult endeavor,since collaborators are not to beunderstood as isolated individuals but as members of a network that has acharacteristic structure of information ﬂows.In order to identify the role ofindividuals in a network one ﬁrst has to know the overall pattern of communicationin the network.Social network analysis is a research methodology developed inanthropology and structural sociology that offers formal techniques to study thestructural patterns of communication networks (Mitchell,1969).Its techniques‘‘provide explicit formal statements and measures of social structural properties thatmight otherwise be deﬁned only in metaphorical terms’’ (Wasserman and Faust,1994).We believe that it is necessary to analyse and understand the structure ofcommunication that evolves and is reproduced in collaboration networks in order tobe able to conclude practical interventions for knowledge management purposes.Although a lot has been written about knowledge management and computersupported cooperative work,little is known about the actual structure of interactionsand dynamics in mobile collaborate work environments.Hence,those contributionscan so far only be marginal to the real-world problems of designing collaborativescenarios (Schoberth and Schrott,2001).One interesting issue at the interfacebetween technology and social communication is the question to what extenttechnological changes affect social practice and communication structures.Do thedifferences between mobile and stationary possibilities to communicate implydifferent interactive patterns between the individuals involved?In other words:dodifferent communication media cause different social structures of communication?3.The experimentIn order to be able to gain information about users’ behaviour in mobile computersupported cooperative work settings,we designed a university experiment.Sixteengraduate students were invited to join an experimental business case project at theDepartment of Information Systems at Frankfurt University.For a period of5 weeks they were given a project task to fulﬁl and ﬁnally present their result to aprofessional audience.3.1.DesignThe experimental setting of the business case was as follows:SDD Inc.(SuperiorDigital Devices),a ﬁctional company,was a Helsinki-based enterprise with 3500employees and annual revenues of $21 billion.Students had to imagine that they hadbeen recruited during a seminar held at University in 2000 and had now beenemployed with SDD Inc.for 3 years.Unfortunately,they had lost track of eachother and were now split over several departments of SDD Inc.(marketing,development,sales and international business).The major task for them was todesign,plan and organize a spontaneous product launch for the ‘‘BPA 998’’ (BetterPerforming Assistant,a new personal digital assistant with telephone functionality)at New Years Eve of 2002 in Frankfurt.Originally,the launch was planned forARTICLE IN PRESSG.Schrott,J.Gl.uckler/Int.J.Human-Computer Studies 60 (2004) 737–752 741CEBIT 2003 in March.But since the main competitor was going to present a newproduct at the GSM World Congress in February 2003,i.e.to gain a ﬁrst-moveradvantage,the presentation had to take place as soon as possible.Unfortunately,allof their superiors were on vacation when the chief executive ofﬁcer (CEO) called fortheir help to plan this event.Each of four departments received instructions abouttheir speciﬁc tasks and the requirements for coordination with the otherdepartments.In addition,the students got a budget limit for the event,which theyhad to split up according to their costs (e.g.catering,sound,speakers’ honoraria).Instructions were designed in order to require an interactive work ﬂow,as thefollowing example illustrates:The development department,e.g.had to specify thetechnical characteristics of the new product in order to enable the marketingdepartment to identify the target customer group and to prepare an invitation list forthe product launch.The total number of participants then had to be communicatedto the international business department,which was responsible for the eventlocation.The sales department,for instance had to calculate the price of the productaccording to the development department’s technical speciﬁcation.Hence,all taskswere highly interrelated and a lot of coordination was required from the students,especially with regard to the allocation of the budget across departments.In addition,rules and incentives were speciﬁed in order to render the experimentalproject more realistic and in order to ensure student commitment.The overall taskwas split up in several sub-tasks,which where enforced by the chief executive ofﬁcer(course supervisor).In case of project-failure,all students would not have been givencredits for the course.A continuous necessity to communicate across departmentswas stimulated through external interventions:Re-scheduling deadlines and budgetreductions served as stress-factors that ensured ongoing inter-group coordination.Inaddition to these sanctions,there was also a clear incentive for commitment to theproject.Students were informed ex ante that at the end a winner team would beawarded an attractive prize.3.2.Technical equipment and communication channelsInteraction between the individuals and the teams was the primary unit of analysisof the project.The electronic communication was facilitated in two ways.Emailmessages could be sent and received either via stationary computer facilities (privateor university lab) and a web-based communication portal (mobile service portal(MSP),see below) or via mobile devices and a web-based communication portal(MSP,see below).To enable the exchange of emails,students were provided with acollaboration portal and mobile devices.We used a mobile communication portalfrom T-Mobile (MSP,MSP) with its architecture being displayed in Fig.1.Theportal provides a typical collaboration functionality based on a Microsoft Exchange2000 server,which is protected by ﬁrewalls,and allows for access using variousdevices.Depending on the attributes of the devices,the MSP generates appropriatestyle sheets to display the different contents.The portal allowed for access acrossvarious channels (personal digital assistant,desktop,phone) and providedcollaboration functionality like email,public folders and short message serviceARTICLE IN PRESSG.Schrott,J.Gl.uckler/Int.J.Human-Computer Studies 60 (2004) 737–752742(SMS)-notiﬁcation.For further information about the technical speciﬁcation of theportal see T-Mobile (2002).We customized the portal to the corporate structure ofthe SDD Inc.Intranet to make the environment as realistic as possible for thestudents.In order to provide students with a 24h possibility to use electronic communica-tion,everybody received a subscriber identiﬁcation module (SIM)-card and a mobiledevice (cf.Fig.2).Eight students received a T-Mobile MDA and eight students acombination of Compaq iPaq H3870 and Nokia 6310 (cf.Fig.2).The T-MobileMDA had an integrated global system for mobile communication module andallowed for transport control protocol/internet protocol connections to the server,the Compaq 6310 was enabled for server connection by providing the students with aNokia 6310 phone with Bluetooth capability.At the initial meeting,we assured thatall students were able to get access to the portal and that no severe technicalproblems remained.The SIM card as well as the mobile federations were free ofcharge for the students.ARTICLE IN PRESSFig.1.Architecture MSP.Fig.2.T-Mobile MDA and Compaq iPaq H387/Nokia 6310 bundle with SIMcards.G.Schrott,J.Gl.uckler/Int.J.Human-Computer Studies 60 (2004) 737–752 7433.3.Data collection and methodsBoth,mobile as well as stationary electronic messages were recorded electronicallyby log ﬁle-analysis.The email log ﬁles went through several steps of datatransformation (Fayyad,1996;Mobasher et al.,2000).All communication ﬂowstowards and fromthe chief executive ofﬁcer were removed fromthe raw data,as wellas ‘delivery-failure-notices’ and administrative questions.Students were instructed torespect a series of conventions on how to use these media:(1) the students were notallowed to use any other than the project email address;(2) all electronic messageshad to be titled in a deﬁned way in order to distinguish administrative questionsfrom content messages,as well as to identify emails sent through the mobile channelmore easily during the data analysis.Besides,students were asked to avoid‘broadcasting’,which means spreading their messages to everybody in the groupalthough they were not directly affected by the message.Apart from the electronic documentation of email messages,students were askedto complete a questionnaire after the project had ended.Here,students evaluated thedifferent communication channels in terms of their usefulness and convenience.Further,they indicated in which situations they used what kind of electronicchannel.We used these data in order to evaluate our results.4.ResultsThe project was carried out during 5 weeks between November 11th and December15th 2002.Although students were allowed to have face-to-face meetings,use mobiletelephones and the SMS,most communication was electronic.Because of the scarceuse of phone calls and SMS messages,these media were dropped out of the analysisand focused exclusively on mobile and stationary email communication.1During thisperiod students interacted intensively within their teams as well as between teams:2745 dyadic interactions were realized via desktop-access and 990 via the mobileclients throughout the 5 weeks of observation.The number of dyadic interactionscounts all communication acts between two individuals.If student x for example,sent a mail to student y and z,the number of dyadic interactions would be two.A density analysis of both communication networks shows that stationaryelectronic communication not only outweighed mobile communication in frequen-cies but also implied a higher density of interrelations (Fig.3).2While stationaryARTICLE IN PRESS1The small number of phone calls might be explained due to higher communication costs:While theSIM cards where free of charge to the students and only allowed data transmission,voice transmission(phone calls) had to be made through private phones and paid individually.The little number of SMSmight be due to the availability of mobile email access.When being equipped with mobile email accessincluding ‘‘always on’’-general packet radio services-functionality,the differences between SMS and usingthe MDA to write short messages is very marginal.In addition to that,operating systems,such as PocketPC Phone Edition allow users to boot their mobile device within seconds.2The network structures have been visualized with the software package Pajek (Batagelj and Mrvar,1998).G.Schrott,J.Gl.uckler/Int.J.Human-Computer Studies 60 (2004) 737–752744emails connected 72% of all possible pairs of collaborators within the projectgroups,the overall density of the mobile-network was just half as much with a valueof 36%.4.1.Mobile vs.stationary messagesThe log ﬁles of stationary and mobile emails contained information on sender andreceiver,date of the mail,subjects and size of the message.In order to investigate thedifference between stationary and mobile messages we analysed the size of theexchanged messages.Emails sent over desktop PCs were far bigger than the mailssent via mobile devices.The average size of a desktop email was 119.5 kb while anaverage mobile email sized only 4.1 kb,which is about thirty times less the volumethan that of desktop messages.Of course,the mobile service portal optimizes mobileemails to reduce data costs by leaving out some graphical elements (buttons).However,this cannot account for the signiﬁcant difference in size.In sum,emailssent over mobile devices were signiﬁcantly smaller than emails sent over a desktopPC.In the questionnaires students reported that,given the inconvenience,they tried tokeep the messages as short as possible when they used mobile devices.In order to geta better understanding of the criteria for the choice of the different media,studentswere asked to assess the effectiveness of mobile and stationary messaging.3On afour-point rating scale (with 4 indicating highest effectiveness) electronic messagesscored less than face-to-face meetings (3.81) which offered the maximum richness ofexchange.However,electronic messages were used far more frequently and thusembraced a large part of the entire interaction within the project group.Therefore,stationary emails scored 3.44 and did not fall much behind the perceivedeffectiveness of meetings.In contrast,mobile emails scored clearly less with only2.38 points on average.Interestingly,meetings and desktop emails only received highmarks (3 and 4),while the evaluation of mobile emails ranged from1 to 4,showing ahigher heterogeneity.ARTICLE IN PRESSFig.3.Network graphs of communication channels.3For reasons of privacy,we did not analyse the content of individual email messages.G.Schrott,J.Gl.uckler/Int.J.Human-Computer Studies 60 (2004) 737–752 745Apart from evaluating the effectiveness of the media,students were asked tobrieﬂy state the main reasons for using stationary and mobile emails.Mobile emailswere mainly sent for quick and spontaneous coordination.Especially when studentswere ‘on the road’ mobile devices allowed themto be up to date and respond quicklyto changes.In all other cases,stationary emails outweighed mobile communicationbecause it was more convenient and allowed the enclosure of attachments,e.g.product speciﬁcations.However,both media were qualiﬁed as weak with regard tobargaining,decision taking,and developing creative ideas.In those instances,students preferred to meet personally in order to make use of the increased richnessof information exchange.4.2.Situation dependenceThe target and work plan of the experiment were challenging for the participants.They had to organize and coordinate themselves in a very professional manner tocomplete their tasks successfully.Especially the splitting up of the global budget intoteam-budgets and the fulﬁlment of deadlines required an intense and faultlessinteraction between the students.Additional stress was imposed on the group byshortening the budget at one stage and advancing the deadline for a milestone atanother stage.The following graph (Fig.4) gives an overview of the communicationactivity along the duration of the seminar.The dotted line indicates the number of dyadic messages sent over a stationarydesktop PC,the solid line reﬂects those which were sent over a mobile device.InARTICLE IN PRESS0501001502002503003501 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33project daynumber of daydic messagesstationary emailsmobile emailsFig.4.Electronic communication over time.G.Schrott,J.Gl.uckler/Int.J.Human-Computer Studies 60 (2004) 737–752746total,the number of desktop emails (2745) exceeded by far the number of mobileemails (990).The distribution of email messages over time shows that the ﬂow ofcommunication was not continuous at one level of intensity but varied considerablyin terms of frequency.Over the 5 week period a number of communication peaks canbe observed as well as a number of days nearly without any message exchanges.However,the distribution of the two communication media was similar over time:mobile and stationary emails followed the same temporal pattern and werecorrelated with r = 0.68 (p o 0.01,N=33).Despite the similar temporal pattern,however,there are various instances,in which the number of mobile messagesprevailed over stationary messages.Fig.5 illustrates the differences between thenumber of interactions.White bars indicate the dominance of stationary emails,black bars the dominance of mobile emails.During the project period,the number of mobile messages exceeded stationaryemails on 5 days:November 13th 2002,November 15th 2002,December 4th 2002,December 7th 2002 and December 16th 2002.What were the conditions that mademobile communication more effective in these instances?Acloser look at the processof task-assignment helps to reconstruct the dominant use of mobile devices.Usually,the supervisor sent emails to the students providing themwith details on the task andthe corresponding deadline.Students were also informed that task completion wasnecessary within the deadline to get the credit points for the course.This constraintwas introduced in order to enforce collaboration and interaction.ARTICLE IN PRESS-60-104090140190123456789101112131415161718192021222324252627282930313233project daynumber of dyadicmessagesFig.5.Daily frequency differences between stationary and mobile email messages.G.Schrott,J.Gl.uckler/Int.J.Human-Computer Studies 60 (2004) 737–752 747The students had to fulﬁl three main tasks.The ﬁrst task was to group themselvesin four teams with four students each.After handing out the login-information forthe portal,the mobile devices and SIMcards on the evening of November 11th,thestudents received an email,which asked themto build teams and report membershipby November 15th.The extensive use of mobile devices on November 13th (ﬁrstwhite bar in Fig.4) is a result of the students acquainting themselves with the mobiledevices and testing for the functionality of the portal.The second peak on November15th was due to the fact that students wanted to get the response fromthe supervisorabout the process of team formation.Since they attended other courses in theuniversity,they checked with their mobile devices in order to be able to immediatelycomment with their colleagues afterwards.The second task was to generate apreliminary version of the event-plan for the product launch.The deadline forsending the document to the CEO was Monday,December 1st,evening.Due to atechnical problem at the server farm of the provider,the mobile access to the portalwas not available for one day so that stationary emails prevailed clearly untilDecember 3rd.The third peak of mobile communication on December 4th was aconsequence of the fact that the draft of one teamwas rejected and a second deadlinefor December 6th was set.The corresponding teamused their mobile devices in orderto quickly spread news and organize their work program for revision.Correspond-ingly,on Sunday,7th the students also used their mobile devices to communicateabout the response about their submitted drafts.The last time that mobilecommunication exceeded stationary emails was on the last day of the course.Againthe same pattern could be observed.After the deadline for the ﬁnal paper onDecember 15th had expired,students wanted to be able to quickly respond to anyresponse that would have affected their work.In sum,mobile emails prevailed over stationary communication under conditionsof stress.Whenever response and mutual coordination were probable and had to bemanaged quickly students used mobile devices in order to be alert and react withoutdelay.More generally it can be concluded that with increasing stress,collaboratorswere more likely to use mobile devices.4.3.Structural attributesApart from differences in frequency,we were interested to see whether the twotypes of communication channels reﬂected different structural patterns of commu-nication.4We used the quadratic assignment procedure in order to check forsystematic differences across the two communication relations and to see whetherdifferent communication relations supported different patterns of interaction(Krackhardt,1987).The quadratic assignment procedure proceeds as follows:ﬁrst,for two observed matrices,stationary and mobile emails,the Pearson correlationcoefﬁcient is calculated.Then the rows and columns of the comparative matrix arepermuted to provide a new,mixed up matrix.Now both matrices are correlatedARTICLE IN PRESS4For a detailed analysis and discussion of the results of the social network analysis see Gl.uckler andSchrott (2003)G.Schrott,J.Gl.uckler/Int.J.Human-Computer Studies 60 (2004) 737–752748again and the r-value is stored away.This permutation-correlation process isrepeated an arbitrarily large number of times (here 2500).The individual r-valuesfromthe permutations generate an empirical reference distribution against which theobserved original r-value is then compared.If fewer than 5%of the r-values fromtherandom correlations are larger than the observed r-value of the original correlation,the correlation is qualiﬁed signiﬁcant at the 0.05 level.The quadratic assignment procedure analysis between mobile and desktop emailsshows an intermediate correlation coefﬁcient (r = 0.418).In all cases the 2500random permutations of the matrices did not produce a single correlation thatexceeded this observed r-value.Therefore,with the signiﬁcance at level 0.01 the twomatrices are statistically associated with each other,which means both communica-tion media reﬂect the same communication pattern.The students who committedthemselves to other students by using desktop emails,were most likely to alsocommit their mobile emails to these students.Although communication spreadacross different media,this does not imply that the different media served differentcommunication relations.Hence,communication exchange displayed a similarstructural pattern across the media.In response to the question raised in Section 2.5this result shows that different communication media do not imply different socialpatterns of interaction.Instead it seems that different media enrich existingcommunication relations and increase the possibilities to reach others.Mobilecommunication,therefore,reﬂects the same kind of social work relations and can beemployed in order to complement and support existing communication networks.5.Summary and further researchResearch about mobile computer supported cooperative work lags behind currentpractices.Mobile interaction and communication processes of cooperative groupsare still poorly understood from a socio-technical perspective.To get a betterunderstanding about the distinct attributes of mobile communication processes,especially exchange of emails in comparison to communication which are initiatedvia desktop PCs we conducted a 5 week cooperative business-case experiment with16 students at the Business-Administration and Economics Faculty,FrankfurtUniversity,Germany.All students were equipped with mobile devices and access to aweb-based communication portal.In contrast to many other experiments,our focuswas not exclusively on the usage of mobile channels of communication.We enabledstudents to choose between various modes of communication,such as sending andreceiving emails via traditional desktop PCs,which allowed for a comparativeanalysis of usage behaviour between these modes.In the experiment we found that emails sent over mobile devices differ from‘traditional’ emails.The higher the demand for voluminous message exchanges,theless likely students chose mobile devices for communication.Interestingly,the use ofmobile communication was highest under conditions of stress.Shortly before andafter the deadlines for the submission of project reports the number of mobile emailsexceeded the number of emails sent via desktop PCs.These insights in user behaviorARTICLE IN PRESSG.Schrott,J.Gl.uckler/Int.J.Human-Computer Studies 60 (2004) 737–752 749should assist designers and engineers to further understand the challenges of mobiledevices for human computer interaction (Dunlop and Brewster,2002).Futureresearch as well as system designers should pay special attention to user groups thatwork in an environment of permanent interaction,changes and mutual recoordina-tion.Despite the difference in size and application of mobile and stationary emailswe found that the different media did not imply different communication patterns.The social structure of mobile communication,i.e.the structure of whocommunicated with whom,did not signiﬁcantly differ from the structure ofstationary email communication.Notwithstanding,this experiment faces a number of limitations:ﬁrst,due to thelimited availability of mobile devices and smart cards the number of students waslimited to 16.Second,students were not charged for using mobile connections.Whilethis may correspond with the provision of mobile communication in bigcorporations,it would be interesting to see how different pricing schemes affectthe use of mobile devices.Third,while students had owned mobile phones for morethan 2 years and were technically interested,they had only little experience withmobile devices for data transmission.Since the use of mobile devices was new formost of the participants it would be helpful to see whether the use of mobilecommunication increases substantially with increased routine.Fourth,students didnot have any additional equipment,as for instance external keyboards.Probably,some of the limitations of user convenience can be reduced with additional tools andwill ‘ease the pain’ of mobile communication.Finally,the students in the experimentalways had the possibility to meet each other on campus and thus avoid mobilecommunication.However,since in many real-world situations collaborators arephysically distributed over large distances,mobile communication may be the onlyviable possibility to exchange information.So we expect mobile communication tohave a more pronounced role in distant work relations.Currently we plan to conductﬁeld studies at selected real-world enterprises and contrast our ﬁndings with thesestudies.AcknowledgementsThe authors are grateful for the technical and ﬁnancial support from T-Mobile,which made this research project possible.ReferencesBatagelj,V.,Mrvar,A.,1998.PAJEK—program for large network analysis.Connections 21,47–57.Bellotti,V.,Bly,S.,1996.Walking away from the desktop computer distributed collaboration andmobility in a product design team.Proceedings of the ACM1996 Conference on Computer SupportedCooperative Work (CSCW‘96),Boston,MA,pp.209–218.Brewster,S.,2002.Overcoming the lack of screen space on mobile computers.Personal and UbiquitousComputing 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